Lubricant composition inhibiting adsorption of alpha-olefin, and method and agent for inhibiting adsorption of alpha-olefin

ABSTRACT

A method for inhibiting adsorption of α-olefin in a lubricant composition to a metal surface is disclosed. The lubricant composition comprises any of oils of Group III, Group IV and polyisobutylenes classified into Group V according to the API base oil classification or a mixture thereof as a base oil, and the α-olefin coexisting in an amount of 1% by mass or less based on the total amount of the composition. The method comprises adding a sarcosinic acid derivative, an aspartic acid derivative or a diethanolamine derivative, or a mixture thereof to the lubricant composition.

FIELD OF THE INVENTION

The present invention relates to a lubricant composition, and more particularly, to improvement of an industrial lubricating oil such as a working oil or a compressor oil.

BACKGROUND OF THE INVENTION

A lubricating oil such as a working oil or a compressor oil cannot obtain good oxidation stability and rust prevention and is difficult to use stably over a long period unless an additive package including a rust inhibitor as an additive is used in the lubricant composition. Therefore, a lubricant composition having desired oxidation stability and rust prevention has been obtained by adding an additive package including a rust inhibitor to a lubricant composition used as a working oil, a compressor oil, or the like.

Although adding such an additive package including a rust inhibitor can usually obtain oxidation stability and rust prevention, with certain types of lubricant compositions, it has been found that even adding a commonly used additive package including a rust inhibitor cannot obtain sufficient oxidation stability and rust prevention.

What causes the phenomenon of not being able to obtain oxidation stability and rust prevention has not been determined, but various studies and investigations have revealed that such a phenomenon is found when a base oil belonging to Group III, Group IV, and polyisobutylenes classified into Group V in the base oil classification of API, or a mixture thereof is used in the base oil of a lubricant composition.

Therefore, various tests and analyses aiming to further elucidate the cause have in summary led to the presumption that this phenomenon is caused by a very small quantity of an α-olefin having a double bond being mixed in the lubricant composition. Alpha-olefins are highly reactive, and presumably have an ill effect on oxidation stability.

The invention of the present application seeks to obtain a lubricant composition and the like having excellent oxidation stability and rust prevention by inhibiting adsorption of a very small quantity of an α-olefin, which has an ill effect as described earlier on oxidation stability and rust prevention in a lubricant composition such as a working oil or a compressor oil, so that the α-olefin has no effect on a metal surface.

Although the present inventors considered that substances having a rust-preventing effect would generally be effective, after testing to confirm the effect of various substances with the object of inhibiting the adsorbing effect of a very small quantity of an α-olefin in a lubricant composition, they concluded that just having a rust-preventing effect did not always mean that a substance would be effective.

Because Group III and Group IV base oils are 90 mass % or more saturated hydrocarbons, the present inventors tried obtaining the desired effect by adding a large quantity of an additive having a rust-preventing effect, and found that because additives have low solubility in base oils and adding a large quantity of an additive is disadvantageous economically, an additive which has an effect by adding a small quantity had to be selected.

They then found that among such additives, using a sarcosinic acid derivative, an aspartic acid derivative, or a diethanolamine derivative gave a lubricant composition having good oxidation stability and rust prevention. Specifically, they achieved the present invention on the basis of the finding that adding such a substance can inhibit the adsorbing effect of an α-olefin mixed in a lubricant composition.

SUMMARY OF INVENTION

Accordingly the present invention provides a lubricant composition comprising any of oils of Group III, Group IV and polyisobutylenes classified into Group V according to the API base oil classification or a mixture thereof as a base oil, and α-olefin coexisting in an amount of 1% by mass or less based on the total amount of the composition, wherein a sarcosinic acid derivative, an aspartic acid derivative or a diethanolamine derivative, or a mixture thereof has been added to the composition.

The present invention further provides a method for inhibiting adsorption of α-olefin in a lubricant composition to a metal surface, the lubricant composition comprising any of oils of Group III, Group IV and polyisobutylenes classified into Group V according to the API base oil classification or a mixture thereof as a base oil, and the α-olefin coexisting in an amount of 1% by mass or less based on the total amount of the composition, which method comprises adding a sarcosinic acid derivative, an aspartic acid derivative or a diethanolamine derivative, or a mixture thereof to the lubricant composition.

The present invention can improve oxidation stability and rust prevention in a lubricant composition by inhibiting the adsorbing effect of a very small quantity an α-olefin mixed in a lubricant composition, and as a result, can obtain an excellent lubricant composition.

DETAILED DESCRIPTION OF THE INVENTION

The base oil of the lubricant composition comprises any of oils of Group III, Group IV and polyisobutylenes classified into Group V according to the API base oil classification or a mixture thereof as a base oil. This means that all or substantially all (i.e. greater than 90 mass % based upon the mass of the base oil) of the base oil is chosen from one or more base oils from Group III, Group IV and polyisobutylenes classified into Group V according to the API base oil classification. The base oil of the lubricant composition in the present invention is, for example, a poly-α-olefin (PAO) belonging to Group IV in the base oil classification of API, a highly hydrogenated and refined high viscosity-index mineral oil belonging to Group III and having little sulphur or unsaturated content, a gas-to-liquid (GTL) base oil, a polyisobutylene belonging to Group V, or an oil mixture of these.

Even using a commonly used package additive comprising a rust inhibitor in a lubricant composition using a base oil comprising such a base oil of Group III, Group IV and polyisobutylenes classified into Group V, may not obtain the desired oxidation stability and rust prevention.

Failure to obtain the desired oxidation stability and rust prevention seems to be due to a very small quantity of α-olefin mixed in the lubricant composition as described earlier.

Group IV PAO are produced by polymerising α-olefins, and such a PAO having an α-olefin mixed in presumably occurs when a very small quantity of some of the α-olefin having a double bond remains unreacted in the compound.

Such an α-olefin adsorbing to a metal surface seems to thwart achieving sufficient oxidation stability and rust prevention. Another possibility is that the α-olefin acts as a nucleus which causes the rust inhibitor to form micelles, leaving it unable to adsorb to a metal surface and function as a rust inhibitor.

Hydrocarbon molecules are isomerised by hydrocracking during production of Group III base oils, but if the partial pressure of hydrogen is insufficient or hydrogenation is incomplete, a very small quantity of an α-olefin is presumably mixed in a lubricant composition using such a base oil.

Polyisobutylene has a long-chain hydrocarbon molecular structure obtained by polymerising isobutene, and is classified as a Group V base oil. A very small quantity of an α-olefin derived from the isobutene used as the raw material is presumably mixed in such a base oil.

‘A very small quantity of an α-olefin is mixed in’ means containing 1 mass % or less of an α-olefin in a lubricant composition. The amount of α-olefin is always greater than 0 mass %, i.e. there is a detectable amount of α-olefin. The iodine value or the bromine value is usually used as an indicator of unsaturated content; JIS K 0070 ‘Test Methods for Acid Value, Saponification Value, Ester Value, Iodine Value, Hydroxyl Value and Unsaponifiable Matter of Chemical Products’ describes the iodine value.

The present invention is effective when the iodine value of a base oil is 1.0 g/100 g or less, preferably 0.02 g/100 g to 1.0 g/100 g, and more preferably 0.09 g/100 g to 1.0 g/100 g. The present invention is also effective when the bromine value is 0.64 g/100 g or less, preferably 0.01 g/100 g to 0.64 g/100 g, and more preferably 0.06 g/100 g to 0.64/100 g.

Adding a sarcosinic acid derivative to a lubricant composition is effective when adding a commonly used additive package including a rust inhibitor cannot obtain sufficient oxidation stability and rust prevention.

Such a sarcosinic acid derivative is indicated by the following formula 1:

R₁ in the formula 1 is a C₁₆₋₂₀ alkyl, and preferably a C₁₇ alkyl.

Such a sarcosinic acid derivative is added to obtain the desired oxidation stability and rust prevention in a lubricant composition.

Although it is unclear whether this effect is due to the sarcosinic acid derivative added to the lubricant composition somehow inhibiting α-olefins mixed in the lubricant composition adsorbing to a metal surface, the result is that the desired oxidation stability and rust prevention are obtained.

Because Group III and Group IV base oils are highly refined and additives usually have low solubility, the sarcosinic acid derivative may be added at from 0.001 to 3 mass %, and preferably from 0.005 to 2 mass %, of the total weight of the lubricant composition to avoid being uneconomical due to adding too much.

A substance which inhibits the adsorption of an α-olefin as described earlier is an aspartic acid derivative. Such as aspartic acid derivative is indicated by the following formula 2.

R₂ and R₃ in the formula 2 are hydrogen or the same or different C₃₋₆ alkyl, alkenyl, or hydroxyalkyl, and preferably may be 2-methylpropyl or tertiary butyl. R₄ is a C₁₋₃₀ alkyl or alkenyl, a C₁₋₃₀ alkyl having an ether bond, or a hydroxyalkyl. Examples are octadecyl, alkoxypropyl, or 3-C₆₋₁₈ hydrocarbonoxy C₃₋₆ alkyl, and more preferably, cyclohexyloxypropyl, 3-octyloxypropyl, 3-isooctyloxypropyl, 3-decyloxypropyl, 3-isodexyloxypropyl, or 3-C₁₂₋₁₆ alkoxypropyl. R₅ is a C₁₋₃₀ saturated or unsaturated carboxylic acid group, or a C₁₋₃₀ alkyl, alkenyl, or hydroxyalkyl. Examples are a propionic acid group or a propionylic acid group.

This aspartic acid derivative may be used at from 0.005 to 3 mass %, and preferably from 0.01 to 3 mass %, to the total weight of the lubricant composition.

A substance which inhibits the adsorption of an α-olefin as described earlier is a diethanolamine derivative. Such a diethanolamine derivative is indicated by the following formula 3.

R₆ in the formula 3 is a C₁₆₋₂₀ alkyl, and preferably a C₁₈ alkyl.

Like the sarcosinic acid derivative, the diethanolamine derivative may be added at from 0.001 to 3 mass %, and preferably from 0.005 to 2 mass %, of the total weight of the lubricant composition.

The α-olefin adsorption inhibitor of the present invention and lubricant compositions using this inhibitor will be described specifically hereinafter by citing examples and comparative examples, but the present invention is not to be taken as limited to these examples.

EXAMPLES

The following substances were prepared to produce the examples and comparative examples.

Base Oil:

PAO8: A poly-α-olefin obtained by polymerising 3-4 C₁₀ α-olefins as the principal ingredient. The iodine value of this PAO8 is at or below the detection limit, indicating that substantially no α-olefins are mixed in.

Common Additive Package Comprising Rust Inhibitor:

Industrial Additive Package (IRGALUBE 2030A, made by BASF): This R&O type industrial additive package contains N-1-naphthylaniline, N,N-bis(2-ethylhexyl)-(4 or 5)-methyl-1H-benzotriazole-1-methylamine, (4-nonylphenoxy)benzoic acid, alkylated diphenylamine, steric-hindered phenol, and acyl sarcosinic acid.

Additive α-Olefin:

The α-olefin in the examples and comparative examples is the reagent 1-octadecene made by Wako Pure Chemical Industries. Because this compound has a molecular weight of 252, the iodine value when calculated in the compound separately is 101 g/100 g, and the bromine value is 63.5 g/100 g. The iodine value derived from the α-olefin in compositions containing 1.0 mass % of 1-octadecene in the examples and comparative examples may be said to be 1.0 g/100 g, and the bromine value may be said to be 0.64 g/100 g.

Additives

1. Sarcosinic acid derivative: Oleyl sarcosinic acid in which R₁ is a C₁₇, indicated by the formula 1

2. Aspartic acid derivative: Mixture of N-1-oxy-3-carbonyloxypropyl-N-3-octyloxypropyl-aspartic acid dibutyl ester, N-1-oxy-3-carbonyloxypropyl-N-3-decyloxypropyl-aspartic acid diisobutyl ester, N-1-oxy-3-carbonyloxypropyl-N-3-dodecyloxypropyl-aspartic acid diisobutyl ester, and N-1-oxy-3-carbonyloxypropyl-N-3-tetradecyloxypropyl-aspartic acid diisobutyl ester indicated by the formula 2 (acid value by the method of JIS K2501: 100 mg KOH/g)

3. Diethanolamine derivative: N-Alkenyldiethanolamine (principal ingredient: N-oleyldiethanolamine) comprising a diethanolamine (tertiary amine compound) in which R₆ is a C₁₈ linear alkyl, indicated by the formula 3 (acid value by the method of JIS K2501: 160 mg KOH/g)

4. Succinic acid derivative: (Tetraisopropenyl)succinic acid and 1,2-propanediol half-ester (acid value by the method of JIS K2501: 160 mg KOH/g)

5. Epoxidized ester: Epoxidized rape seed fatty acid 2-ethylhexyl ester

6. Calcium salicylate: Calcium content: 8 mass %, acid value by the method of JIS K2501: 230 mg KOH/g

7. Calcium sulphonate: Calcium content: 2.1 mass %, acid value by the method of JIS K2501: 0.2 mg KOH/g

8. Alkyl ether carboxylic acid: Acid value by the method of JIS K2501: 120 mg KOH/g

Example 1

A lubricant composition comprising 98.4 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.1 mass % of the sarcosinic acid derivative.

Example 2

A lubricant composition comprising 98.0 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.5 mass % of the sarcosinic acid derivative.

Example 3

A lubricant composition comprising 98.0 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.5 mass % of the aspartic acid derivative.

Example 4

A lubricant composition comprising 98.0 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.5 mass % of the diethanolamine derivative.

Comparative Example 1

A lubricant composition comprising only a base oil consisting of 100 mass % of PAO8.

Comparative Example 2

A lubricant composition comprising 99.5 mass % of PAO8, and 0.5 mass % of a commonly used package additive including a rust inhibitor.

Comparative Example 3

A lubricant composition comprising 98.5 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, and 1.0 mass % of the α-olefin.

Comparative Example 4

A lubricant composition comprising 98.4 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.1 mass % of the succinic acid derivative.

Comparative Example 5

A lubricant composition comprising 98.0 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.5 mass % of the succinic acid derivative.

Comparative Example 6

A lubricant composition comprising 98.0 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.5 mass % of the epoxidized ester.

Comparative Example 7

A lubricant composition comprising 98.4 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.1 mass % of calcium salicylate.

Comparative Example 8

A lubricant composition comprising 98.0 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.5 mass % of calcium salicylate.

Comparative Example 9

A lubricant composition comprising 98.4 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.1 mass % of calcium sulphonate.

Comparative Example 10

A lubricant composition comprising 98.0 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.5 mass % of calcium sulphonate.

Comparative Example 11

A lubricant composition comprising 98.0 mass % of PAO8, 0.5 mass % of a commonly used package additive including a rust inhibitor, 1.0 mass % of the α-olefin, and 0.5 mass % of the alkyl ether carboxylic acid.

Tests:

Rust-proofing test: Based on JIS K2510, after 300 ml of a test oil were collected in a vessel set up in a constant-temperature bath, stirred at 1000 revolutions per minute, and heated to 60° C., test pieces made of iron were inserted into the test oil, which was further combined with 30 ml of artificial seawater and stirred while maintained at 60° C. for 24 hours, after which the test pieces were removed and evaluated visually for whether or not rust had occurred and, if so, to what extent.

The test evaluation was based on the following criteria.

No rust found . . . None (passed: O)

Slight rust found . . . Slight (not passed: x)

Moderate rust found . . . Moderate (not passed: x)

Heavy rust found . . . Heavy (not passed: x)

Tables 1 and 2 show the compositions of the examples and the comparative examples, and the results of the rust-proofing test.

TABLE 1 Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 1 Ex. 2 Ex. 3 PAO8 98.4 98.0 98.0 98.0 100 99.5 98.5 Package including a rust inhibitor 0.5 0.5 0.5 0.5 0.5 0.5 Sarcosinic acid derivative 0.1 0.5 Asparaginic acid derivative 0.5 Diethanolamine derivative 0.5 Succinic acid derivative Epoxidized ester Calcium salicylate Calcium sulphonate Alkyl ether carboxylic acid α-Olefin 1.0 1.0 1.0 1.0 1.0 Rust-proofing test None None None None Heavy None Moderate (∘) (∘) (∘) (∘) (x) (∘) (x)

TABLE 2 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 PAO8 98.4 98.0 98.0 98.4 98.0 98.4 98.0 98.0 Package including a 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 rust inhibitor Sarcosinic acid derivative Asparaginic acid derivative Diethanolamine derivative Succinic acid 0.1 0.5 derivative Epoxidized ester 0.5 Calcium salicylate 0.1 0.5 Calcium sulphonate 0.1 0.5 Alkyl ether carboxylic 0.5 acid α-Olefin 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Rust-proofing test Moderate Heavy Heavy Heavy Moderate Heavy Heavy Heavy (x) (x) (x) (x) (x) (x) (x) (x)

Discussion

With Comparative Example 1 which comprised only the base oil of PAO8, heavy rust occurred.

Comparative Example 2 was produced by combining Comparative Example 1 with 0.5 mass % of a commonly used package additive including a rust inhibitor, and as a result, no rust was found.

Because Comparative Example 3 was produced by combining Comparative Example 2 with 1.0 mass % of the α-olefin, (moderate) rust was found even though the lubricant composition contained a package additive including a rust inhibitor when the α-olefin was mixed in.

Example 1 was produced by combining Comparative Example 3, having α-olefin mixed in, with 0.1 mass % of the sarcosinic acid derivative, with which, no rust was found to occur.

Example 2 was produced by combining the same with 0.5 mass % of a sarcosinic acid derivative, with which, no rust was found to occur.

Example 3 was produced by combining Comparative Example 3, having α-olefin mixed in, with 0.5 mass % of the aspartic acid derivative, with which, no rust was found to occur.

Example 4 was produced by similarly combining Comparative Example 3, having α-olefin mixed in, with 0.5 mass % of the diethanolamine derivative, with which, no rust was found to occur.

Thus, even with an α-olefin mixed in a lubricant composition, adding a small quantity of a sarcosinic acid derivative, an aspartic acid derivative, or a diethanolamine derivative seemed to inhibit the adsorbing effect of the α-olefin, and achieve a rust inhibiting effect.

Comparative Example 4 was produced by combining Comparative Example 3, having α-olefin mixed in, with 0.1 mass % of the succinic acid derivative, with which, (moderate) rust was found to occur. Comparative Example 5 was produced by combining the same with 0.5 mass % of the succinic acid derivative, with which, (moderate) rust was found to occur.

Comparative Example 6 was produced by combining Comparative Example 3, having α-olefin mixed in, with 0.5 mass % of the epoxidized ester, with which, (heavy) rust was found to occur.

Comparative Example 7 was produced by combining Comparative Example 3, having α-olefin mixed in, with 0.1 mass % of calcium salicylate, with which, (heavy) rust was found to occur.

Comparative Example 8 was produced by combining the same with 0.5 mass % of calcium salicylate, with which, (moderate) rust was found to occur.

Comparative Example 9 was produced by combining Comparative Example 3, having α-olefin mixed in, with 0.1 mass % of calcium sulphonate, with which, (heavy) rust was found to occur. Comparative Example 10 was produced by combining the same with 0.5 mass % of calcium sulphonate, with which, (heavy) rust was also found to occur.

Comparative Example 11 was produced by combining Comparative Example 3, having α-olefin mixed in, with 0.5 mass % of the alkyl ether carboxylic acid, with which, (heavy) rust was found to occur.

Thus, when added at a quantity usually considered suitable, a succinic acid derivative, an epoxidized ester, calcium salicylate, and calcium sulphonate, which are usually considered to have a rust inhibiting effect and are used to obtained such an effect, could not prevent worsening of rust caused by an α-olefin being mixed in. 

1. A lubricant composition comprising any of oils of Group III, Group IV and polyisobutylenes classified into Group V according to the API base oil classification or a mixture thereof as a base oil, and α-olefin coexisting in an amount of 1% by mass or less based on the total amount of the composition, wherein a sarcosinic acid derivative, an aspartic acid derivative or a diethanolamine derivative, or a mixture thereof has been added to the composition.
 2. A lubricant composition according to claim 1, wherein the sarcosinic acid derivative is indicated by the following formula 1:

wherein R₁ is a C₁₆₋₂₀ alkyl; wherein the aspartic acid derivative is indicated by the following formula 2:

wherein R₂ and R₃ are hydrogen or the same or different C₃₋₆ alkyl, alkenyl, or hydroxyalkyl; R₄ is a C₁₋₃₀ alkyl or alkenyl, a C₁₋₃₀ alkyl having an ether bond, or a hydroxyalkyl; and R₅ is a C₁₋₃₀ saturated or unsaturated carboxylic acid group, or a C₁₋₃₀ alkyl, alkenyl, or hydroxyalkyl; and wherein the diethanolamine derivative is indicated by the following formula 3:

wherein R₆ is a C₁₆₋₂₀ alkyl.
 3. A lubricant composition according to claim 1, wherein the amount of the sarcosinic acid derivative or the diethanolamine derivative is from 0.001 to 3% by mass based on the total amount of the composition, or the amount of the aspartic acid derivative is from 0.005 to 3% by mass based on the total amount of the composition.
 4. A method for inhibiting adsorption of α-olefin in a lubricant composition to a metal surface, the lubricant composition comprising any of oils of Group III, Group IV and polyisobutylenes classified into Group V according to the API base oil classification or a mixture thereof as a base oil, and the α-olefin coexisting in an amount of 1% by mass or less based on the total amount of the composition, which method comprises adding a sarcosinic acid derivative, an aspartic acid derivative or a diethanolamine derivative, or a mixture thereof to the lubricant composition.
 5. A method for inhibiting the adsorption of α-olefin according to claim 4, wherein the sarcosinic acid derivative is indicated by the following formula 1:

wherein R₁ is a C₁₆₋₂₀ alkyl; wherein the aspartic acid derivative is indicated by the following formula 2:

wherein R₂ and R₃ are hydrogen or the same or different C₃₋₆ alkyl, alkenyl, or hydroxyalkyl; R₄ is a C₁₋₃₀ alkyl or alkenyl, a C₁₋₃₀ alkyl having an ether bond, or a hydroxyalkyl; and R₅ is a C₁₋₃₀ saturated or unsaturated carboxylic acid group, or a C₁₋₃₀ alkyl, alkenyl, or hydroxyalkyl; and wherein the diethanolamine derivative is indicated by the following formula 3:

wherein R₆ is a C₁₆₋₂₀ alkyl.
 6. A method for inhibiting adsorption of α-olefin according to claim 4, wherein the amount of the sarcosinic acid derivative or the diethanolamine derivative added is from 0.001 to 3% by mass based on the total amount of the composition, or the amount of the aspartic acid derivative added is from 0.005 to 3% by mass based on the total amount of the composition. 